In "open" surgical procedures, the surgeon gains access to work inside the body by cutting large incisions through the body wall, then stretching the overlying tissue apart to provide visibility and room to manipulate his hands and instruments. Vital structures are generally held away from the surgical site and shielded from instruments by being covered with cloth pads. The surgeon can touch and manipulate the tissues. As the surgeon manipulates, cuts and dissects tissues, he controls the resultant bleeding by blotting or suctioning away the accumulating blood, enabling him to see the bleeding vessels and clamp and tie them off.
The creation of a large opening in the patient's body tissue greatly increases the risk of surgery to the patient's health, by increasing the probability of complications. Those complications can arise not only from treatment of the target tissue, i.e., that tissue necessitating the surgery, but also from the trauma caused to adjacent tissue in creating an opening providing the surgeon with access to the target tissue. Once the internal tissue is operated upon, the surgeon faces the time-consuming task of closing up the surgical site. In addition, the patient may require extensive post-operative care and an extensive hospital stay.
Development of the endoscope, a miniaturized television camera that is inserted through a puncture wound in the body wall to provide a video image of the inside of the body cavity, has enabled surgeons to perform surgery using specially designed surgical instruments that are inserted through other small puncture wounds. Some previously known devices have been constructed that enable a surgeon to operate on internal tissue while viewing manipulation of the instrument through an endoscope. One such device is described in Falk, U.S. Pat. No. 4,994,024. Such previously known endoscopic instruments have several disadvantages, especially the inability to effectively stem blood flow from incised tissue.
Endoscopic surgery no longer requires cutting a large gaping incision through the body wall, and permits patients to undergo some major surgeries practically pain-free, with little or no post-operative hospital stay. However, in performing endoscopic surgery the surgeon forgoes manual access to the tissues being operated upon. In doing so, he gives up his traditional means of controlling bleeding by clamping and tying off transected blood vessels. Consequently, in endoscopic surgery it is important that tissues that are cut must not bleed.
Hemostatic surgical techniques are known for reducing the bleeding from incised tissue during open surgical procedures, i.e., where overlying body tissue is severed and displaced to gain access to internal organs. Such techniques include electrosurgery, that is, passing a high frequency or radio frequency current through the patient's tissue between two electrodes for cutting and coagulating the blood vessels contained within the tissue. The current passing through the tissue causes joulean (ohmic) heating of the tissue as a function of the current density and the resistance of the tissue through which the current passes. This heating dehydrates the tissues and denatures the tissue proteins to form a coagulum which seals bleeding sites, so that the body's own collagen is reformed as a glistening white layer on the cut surface, sealing the tissues against bleeding.
Heretofore, endoscopic electrosurgical techniques have been limited primarily to monopolar devices. Previously known monopolar electrosurgical instruments employ a small electrode at the end of a handle in the surgeon's hand and a large electrode plate beneath and in contact with the patient. Only one of the two electrodes required to complete the electrical circuit is manipulated by the surgeon and placed on or near the tissue being operated on. The other electrode is the large plate beneath the patient. A power supply impresses high frequency voltage spikes of thousands of volts between the two electrodes of the electrosurgical instrument, sufficient to cause arcing from the small operating electrode the surgeon holds to the most proximate tissues, then through the patient to the large electrode plate beneath the patient. In the patient, the electrical current becomes converted to heat; hottest in the tissues immediately below the small hand-held electrode where the currents are most concentrated. Devices, such as the forceps Model No. A5261, and electrode Model No. A5266, available from Olympus Corporation Medical Instrument Division, Milpitas, Calif., are representative of such monopolar instruments.
A principal disadvantage of monopolar electrocautery is that current flows completely through the patient. These high voltage electrical currents may arc from the small electrode to nearby non-targeted vital structures, or may follow erratic paths as they flow through the patient's body, thereby causing damage to tissues both near and at some distance from the electrode.
While monopolar devices have proven useful in open surgical procedures, where the surgeon is able to view the effects of the current arc, the problems encountered in open surgical procedures become even more important in endoscopic surgical applications. In particular, when using a monopolar device endoscopically, the surgeon's view of the electric arc generated by the instrument is restricted by the limited field of view provided by the endoscope. Consequently, aberrant current arcs--the existence of which the surgeon may not even be aware--can cause deep tissue necrosis and inadvertent damage to adjacent tissue masses.
The foregoing limitation has proved especially dangerous for surgeries performed in the abdomen, and in the vicinity of the peritonea and bowel wall. Practical experience has established that aberrant current arcs generated by endoscopic monopolar devices can cause perforation of the adjacent bowel wall when used on abdominal tissue masses. While such damage typically is not apparent to the surgeon during the procedure, it may later be manifested as peritonitis, which results in death in as many as 25% of all such cases.
Bipolar electrosurgical devices for open surgical procedures are known to enable the surgeon to obtain hemostasis in precise local areas without also heating and causing undesirable trauma to adjacent tissue. Bipolar devices have two electrodes closely spaced together so that current flow is confined to the tissue disposed between the electrodes. Heretofore, such instruments have had limited use in endoscopic applications because of the inherent problem of electrically isolating the high voltage electrodes while providing an instrument small enough for use with conventional trocar tubes--typically 5 to 10 mm in diameter. One such device is described in Tischer U.S. Pat. No. 4,655,216. The complicated structure of the device described in that patent illustrates the difficulty encountered in providing the requisite isolation of the electrodes. A second such device is the Olympus Model O5127 bipolar endoscopic forceps, available from Olympus Corporation Medical Instrument Division, Milpitas, Calif.
A further disadvantage inherent in all previously known monopolar and bipolar electrosurgical devices is that of coagulum buildup on the working surfaces of the device. Previously known power supplies used in electrosurgical applications have generally provided high voltage-low current power outputs, which poorly match the impedance of the tissue over the range of conditions typically encountered in electrosurgery. This mismatch, in combination with the arcing characteristic of previously known instruments, leads to charring of the tissue and excessive coagulum buildup on the instrument surfaces.
Yet another difficulty encountered in endoscopic surgery is the limited range of motion available to the surgeon at the surgical site. In particular, because of the relatively small incision through which the instruments are inserted for endoscopic procedures, the surgeon's range of movement of the instrument is greatly restricted.
It would therefore be desirable to provide bipolar electrosurgical instruments for hemostatically severing or manipulating tissue in endoscopic surgical procedures that overcome these disadvantages of such previously known instruments. Such instruments would enable a large number of operations to be carried out endoscopically, thereby reducing the need and risk of open surgical procedures.